With the ever decreasing supply of landfill space, disposal of worn-out vehicle tires is becoming an increasingly significant problem. Over 250 million such tires were scrapped in the U.S. in 1992. Although some spent tires are recycled to be used in pavement and others are burned as boiler fuel, more than 80% are simply dumped in landfills.
Dumping used tires in landfills is a significant waste of recyclable resources. It has been known for many years that tires may be recycled by pyrolysis to obtain valuable by-products. Pyrolysis, generally speaking, is the thermal distillation or decomposition of a substance. In the case of tires, this process is carried out in a slight vacuum at temperatures between 1000.degree. F. and 2000.degree. F.
By recycling the tires through pyrolysis, it is possible to recover substantial amounts of heating oil, producer gas, carbon black and scrap steel. In particular, it is expected that using the apparatus described herein it will be possible to recover approximately 900 lbs of heating oil, 750 lbs of carbon black, 250 lbs of producer gas and 100 lbs of scrap steel from each ton of tires. Since the average used tire weighs 17.4 lbs, the potential production of tire by-products is enormous.
Although many machines have been designed to recycle used tires through pyrolysis, none have been entirely successful. One problem with many previous machines involves the presence of particulate matter in the gas that is extracted from the tires. The particulate matter--primarily carbon dust--accumulates on fittings, vents and flame arresters, which can obstruct passages and create substantial danger of explosion.
Another drawback to known pyrolysis machines involves oil contamination in the carbon black which destroys the commercial value thereof. In order to produce high quality carbon black, virtually all oil must be removed. In most known pyrolysis machines, the oil vapor released from the pyrolyzed material is drawn, at least partially, through or past the carbon black product, thus contaminating it with oil residue.
Material handling also has presented substantial challenges in known pyrolysis machines. When shredded tires are processed, the residual steel strands and natural stickiness of the heated rubber combine to make transporting the material to be pyrolyzed a significant challenge. Thus, a persistent problem with known machines is "bailing-up" of the shredded tire pieces leading to jamming of the auger used to convey them. The shredded pieces may also agglomerate in the bridge openings or plug pipes.
Accordingly, it is an object of the present invention to provide a pyrolysis system to efficiently process used vehicle tires and other hydrocarbon-based material.
Another object of the invention is to provide such a system with low environmental emissions.
One more object of the present invention is to provide a pyrolysis system in which the gas and oil vapor generated is prefiltered to remove particulate matter.
Yet another object is to provide a system that is able to continuously process spent tires.
An additional object of the present invention is to provide a pyrolysis system that produces high-grade carbon black as a byproduct of the pyrolytic decomposition of hydrocarbon material.